1. Field of the Invention
This invention relates to a Venetian blind, and more particularly to a cord winding device for a Venetian blind.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a Venetian blind disclosed in U.S. Pat. No. 406,995 includes a head rail 1, a bottom rail 2, a plurality of slats 3 disposed between the head rail 1 and the bottom rail 2, two pull cords 4 connected to the head rail 1 and the bottom rail 2 and extending through the slats 3, and a cord winding device 5 mounted in the head rail 1.
The cord winding device 5 includes a support 6 fixed in the head rail 1, a resilient driving unit 7 mounted on the support 6, and a braking unit 8.
The resilient driving unit 7 includes first and second reels 701, 702, a driving wheel 703 disposed between the first and second reels 701, 702, a spring winding wheel 704 disposed between the driving wheel 703 and the second reel 702, and a spiral spring 705 disposed between the driving wheel 703 and the spring winding wheel 704. Four gears 706 are connected respectively to the first and second reels 701, 702, the driving wheel 703, and the spring winding wheel 704. Any two adjacent gears 706 mesh with each other.
The braking unit 8 includes a braking wheel 801 and a braking mechanism 802 disposed between the braking wheel 801 and one of the pull cords 4 for controlling geared connection between the braking wheel 801 and the first reel 701.
The bottom rail 2 can be stopped at any desired height. However, if the size of the Venetian blind is comparatively large such that the total weight of the slats 3 and the bottom rail 2 is greater than the return force of the spiral spring 705, since the bottom rail 2 is not braked during lowering of the bottom rail 2, downward movement speed of the slats 3 and the bottom rail 2 is relatively quick so that the bottom rail 2 may cause damage to a person or an article disposed under the Venetian blind, thereby affecting adversely safety during use.
To overcome this drawback, in an improved Venetian blind disclosed in CN202788572, the applicant proposes to add a unidirectional clutch and a damping unit to the Venetian blind disclosed in U.S. Pat. No. 406,995, so as to retard downward movement of the bottom rail 2, thereby increasing safety during use. However, since a relatively large space is required for operation of the braking mechanism, its volume needs to be reduced.